In recent years, various communication systems have been developed along with an increase in requirements for communications and progress in communication technologies. One of such communication systems is a satellite broadcasting system using a broadcasting satellite or a communication satellite on the geostationary orbit. The satellite broadcasting system has an advantage that it can provide an information broadcasting service to a wide service area without any large-scale infrastructure on the ground.
A satellite broadcasting system in operation to date is an analog system which multiplexes a plurality of channels by frequency division multiplex (FDM: Frequency Division Multiplex). In a system of this type, however, the degree of channel multiplex per frequency is low, so this system cannot meet a requirement for more channels, which has arisen along with recent advances in multimedia technologies.
Recently, digital satellite broadcasting systems have been extensively studied and developed. In this case, use of, e.g., orthogonal frequency division multiplex (OFDM: Orthogonal Frequency Division Multiplex) or code division multiplex (CDM: Code Division Multiplex) has been examined as channel multiplex schema.
However, these multiplex schema have various problems to be solved before they are applied to the satellite broadcasting system. Especially, CDM requires a time as long as, e.g., ten-odd seconds until the receiver establishes spreading code synchronization for a broadcasting signal. For this reason, the receiver needs a long time from the start to completion of channel switching. The viewers must wait for a long time every time the channel is switched and feel displeased. In some cases, important information may be lost during the channel switching period, and a measure is necessary.
Considering the above problems, a demand has arisen for a satellite broadcasting system which allows the broadcasting receiver to quickly switch the channels for the received multiplexed broadcasting signals at a high response speed, thereby improving the convenience for the viewers.
In Japan, satellite broadcasting systems using a BS (Broadcasting Satellite) and a CS (Communication Satellite) have already been put into practice, and digital broadcasting has also been started. In other countries as well, satellite broadcasting systems of almost the same scale have been developed and put into practice.
However, these satellite broadcasting systems require use of a parabolic antenna having a diameter of about 40 to 50 cm or a planar array antenna almost equal in size as a reception antenna. In addition, unless the antenna is precisely directed to the satellite, no sufficient gain is obtained, and reception is disabled.
These systems assume indoor reception/viewing, so it is hard to provide a satellite broadcasting receiver using a simple antenna system meeting requirements for use on a mobile or use as a portable device. An apparatus meeting these requirements can effectively function as a means for providing urgent information in disasters or the like and its implementation in the near future is awaited.
Various types of satellite broadcasting systems, receivable by a receiver using a simple antenna system, or satellite broadcasting receivers have been proposed to cope with the requirements. However, since these systems or apparatuses use a very high frequency in, e.g., the S band, and radio waves have high linear propagation properties, the radio waves may be shielded by a small obstacle such as an electrical wire in an extreme case. Generally, when the reception terminal is moving, small obstacles frequently enter between the broadcasting satellite and the reception terminal. This repeatedly generates hits a nd largely influences the reception quality.
From this viewpoint, a demand has a risen for a radio receiver, a radio broadcasting system, and a radio broadcasting apparatus capable of minimizing the influence of hits due to obstacles and obtaining a satisfactory reception quality.
A direct wave from the satellite cannot be received in an area behind buildings. To solve this problem, conventionally, a public antenna having a large diameter is arranged on the rooftop of a high-rise building or a pylon. The radio signal from the satellite is received and amplified by this public antenna. This received radio signal is distributed to the receivers of users behind buildings through coaxial cables or optical cables. With this arrangement, users behind buildings, who cannot receive the radio signal from the satellite, can also completely receive transmission information from the satellite.
However, such a public reception system requires large-scale construction and enormous cost because cables must be laid to all users. Recently, information transmission using the satellite broadcasting system not only to fixed stations but also to mobile stations has been proposed. In this case, users as fixed stations behind buildings can receive information from the satellite through the above-described public reception system. However, mobile stations behind the buildings cannot receive information from the satellite because no coaxial cables or optical cables can be laid to the mobile stations.
Under the circumstance, a demand has arisen for a satellite broadcasting system capable of making not only a fixed station but also a mobile station in an area behind buildings, where a radio signal from the satellite cannot be directly received, properly receive the radio signal without preparing large-scale equipment, thereby realizing an inexpensive and effective gap filler, and a gap filler apparatus therefor.
In satellite broadcasting systems of any types, when the number of broadcasting channels is increased, the output requirement for a repeater-side power amplifier on the satellite becomes high accordingly, so it is difficult to require an increase in number of broadcasting channels.
In view of the foregoing, a demand has arisen for a satellite broadcasting system and a reception terminal, which can easily increase the number of channels with a simple arrangement.
The satellite broadcasting systems require use of a parabolic antenna having a diameter of about 40 to 50 cm or a planar array antenna almost equal in size as a reception antenna. In addition, unless the antenna is precisely directed to the satellite, no sufficient gain is obtained, and reception is disabled. These systems assume indoor reception/viewing, so it is hard to provide a satellite broadcasting receiver using a simple antenna system meeting requirements for use on a mobile or use as a portable device. An apparatus meeting these requirements can effectively function as a means for providing urgent information in disasters or the like and its implementation in the near future is awaited.
Under the circumstance, a demand has arisen for a satellite broadcasting system, receivable by a receiver using a simple antenna system meeting requirements for use on a mobile or use as a portable device, and a satellite broadcasting receiver.
Development of a satellite broadcasting receiver for receiving the above-described satellite broadcasting on a mobile such as an automobile is prevalent recently.
To receive the satellite broadcasting on a mobile such as an automobile, the driver must switch the reception channel in a number of channels, as described above. Since this channel selection operation is cumbersome and distracts the driver from driving, a traffic accident may be caused.
To prevent this danger, various danger prevention methods have been proposed conventionally but any conclusive methods has not appeared. Therefore, a demand has arisen for a satellite broadcasting receiver capable of switching the reception channel without distracting the driver from driving.
Music for stimulating the driver sometimes contributes to prevent driving asleep. However, depending on the degree of fatigue of the driver, monotonous music may make the driver sleep, resulting in an adverse effect. This applies not only to the drivers of automobiles but also to operators steering various mobiles.
From this viewpoint, a demand has arisen for a satellite broadcasting receiver capable of switching the reception channel without distracting the driver of a mobile from driving. Also, a demand has arisen for a satellite broadcasting receiver capable of controlling reception channel switching in accordance with the fatigue state of the driver to prevent a traffic accident.
Accordingly, it is an object of the present invention to provide a satellite broadcasting system allowing a broadcasting receiver to quickly switch the channels of received multiplexed broadcasting signals at a high response speed, thereby improving the convenience for a viewer.
It is another object of the present invention to provide a radio receiver, a radio broadcasting system, and a radio broadcasting apparatus capable of minimizing the influence of hits due to obstacles and obtaining a satisfactory reception quality.
It is still another object of the present invention to provide a satellite broadcasting system capable of making not only a fixed station but also a mobile station in an area behind buildings, where a radio signal from the satellite cannot be directly received, properly receive the radio signal without preparing large-scale equipment, thereby realizing an inexpensive and effective gap filler, and a gap filler apparatus therefor.
It is still another object of the present invention to provide a satellite broadcasting system and a reception terminal, which can easily increase the number of channels with a simple arrangement.
It is still another object of the present invention to provide a satellite broadcasting system capable of receiving a signal by a receiver using a simple antenna system meeting requirements for not only indoor use but also use on a mobile or use as a portable device, and a satellite broadcasting receiver.
It is still another object of the present invention to provide a satellite broadcasting receiver capable of switching the reception channel without distracting the driver of a mobile from driving. It is still another object of the present invention to provide a satellite broadcasting receiver capable of controlling reception channel switching in accordance with the fatigue state of the driver to prevent a traffic accident.